1. Field of the Invention
The present invention relates to an electric parking brake device using an electric motor as power source and capable of bringing parking brakes into a braking state by the rotation of the electric motor in a positive-going direction but into a braking release state by the rotation of the electric motor in a negative-going direction.
2. Discussion of the Related Art
As electric parking brake devices of this kind, there has been known one which is described in Japanese unexamined, published patent application No. 2005-16600. The device is of the type that the reversible rotational motion of an electric motor is converted by a conversion mechanism into a reciprocating linear motion and that respective parking brakes are operated by a pair of cables whose respective one ends are connected to opposite end portions of an equalizer which is pivotably carried at its center part on a nut serving as an output section of the conversion mechanism. In the electric parking brake device of this type, the respective parking brakes can be operated by the same power at all times by the action of the equalizer whose center part is pivotably carried on the nut.
Further, as parking brakes for use together with the electric parking brake device, there has been known a technology which is disclosed in Japanese unexamined, published patent application No. 2001-173692. The parking brakes B disclosed there are of the type that a drum brake for each parking brake is incorporated inside a disc brake, and as shown in FIGS. 5 and 6, is provided with a first toggle link 36 and a second toggle link 37 which are coupled to be pivotable relative to each other by means of a connection pin 38 extending in parallel to a backing plate 30. A cable 20 (or 25) is inserted into each parking brake B from a cable insertion hole 31a of an anchor member 31 secured to the backing plate 30, and a latch or clasp member 39 is secured to the end of an inner wire 22 (or 27) of each cable 20 (or 25). Thus, each parking brake B is operable to expansively open brake shoes by drawing the inner wire 22 (or 27) with the clasp member 39 being hung on a biforked cable hooking portion 36a of the first toggle link 36. Reference numbers 25, 26 and 27 in FIGS. 5 and 6 denote a cable, an outer tube and an inner wire for the other parking brake (not shown).
In each parking brake B, since the clasp member 39 is placed inside the second toggle link 37 taking a narrow U-letter shape in cross-section as viewed from the right or left in FIG. 5, it is impossible by hand to grip and draw the clasp member 39 and to hang the same on the cable hooking portion 36a of the first toggle link 36. For this reason, hooking the clasp member 39 on a bottom portion of the cable hooking portion 36a is carried out as follows. That is, the clasp member 39 at the end of the inner wire 22 (or 27) is inserted by hand into the cable insertion hole 31a with the outer tube 21 (or 26) of the cable 20 (or 25) being gripped, and the inner wire 22 (or 27) is bent as indicated by the two-dot-chain line 39A to be moved along arc-shape guide surfaces 36c which are formed at outer edge portions of the biforked cable hooking portion 36a of the first toggle link 36. Thus, when the clasp member 39 gets over prominent portions 36b formed at outer ends of the cable hooking portion 36a, the inner wire 22 (or 27) comes to fall into a groove portion 36d (refer to FIG. 6) formed in the biforked cable hooking portion 36a owing to its elasticity. A play which is produced between the clasp member 39 and the bottom portion of the cable hooking portion 36a is removed by drawing the inner wire 22 (or 27) back inside the outer tube 21 (or 26), whereby the clasp member 39 is seated on the bottom portion of the cable hooking portion 36a. 
In order to enable the hanging work to do, the protruding amount of each clasp member 39 from the extreme end of the outer tube 21 (or 26) has to be such a length that enables the clasp member 39 to get over the prominent portions 36b of the first toggle link 36 in the state that the extreme end of each outer tube 21 (or 26) is held in contact with the bottom portion around the associated cable insertion hole 31a, as indicated by the solid line in FIG. 5. On the other hand, in order to downsize the electric parking brake device for lower manufacturing cost, it is necessary to downsize the conversion mechanism and a housing accommodating the same. In this connection, the hanging work is done in the state that the equalizer has been returned by the electric motor to an extreme position toward the parking brake B side and hence that the clasp members 39 at the ends of the inner wires 22, 27 have been protruded from the outer tubes 21, 26 through the largest amounts.
In the foregoing prior art, in order to hang the clasp member 39 of each inner wire 22 (or 27) on the cable hooking portion 36a of the first toggle link 36, the outer tube 21 (or 26) of each cable 20 (or 25) is gripped by hand and is drawn to insert the clasp member 39 at the end of the inner wire 22 (or 27) into the cable insertion hole 31a. At this time, the clasp member 39 is first brought into contact with the start portions of the guide surfaces 36c of the first toggle link 36, and therefore, a reaction force is generated which urges the inner wire 22 (or 27) to be pushed back into the outer tube 21 (or 26). On the other hand, because the equalizer of the electric parking brake device is still pivotable relative to the housing within a certain angular extent even with itself having been returned to the extreme position toward the parking brake B side, the reaction force causes the equalizer to pivot with the result that the inner wire 22 (or 27) is pushed back into the outer tube 21 (or 26) by a distance H1 (not shown) corresponding to the angular extent. Accordingly, the distance between the end portion of each outer tube 21 (or 26) and the root end of each clasp member 39 which distance is required to hang each clasp member 30 on the cable hooking portion 36a as mentioned earlier with the end portion of the outer tube 21 (or 26) being in abutting contact with the bottom portion around the cable insertion hole 31a becomes the sum of the aforementioned distance H1, a distance H2 (shown in FIG. 5) between the bottom portion of the cable hooking portion 36a and the extreme ends of the prominent portions 36b and another distance H3 (also shown in FIG. 5) between the end of the outer tube 21 (or 26) and the bottom portion of the cable hooking portion 36a. 
However, in the foregoing prior art, when the inner wires 22, 27 of the cables 20, 25 are to be drawn for bringing the parking brake B into the braking state, the electric motor is rotated in the positive-going direction, and the conversion mechanism is operated so that the equalizer having been returned to the extreme position through the largest amount toward the parking brake B side is moved in a direction opposite to the parking brake B side. At this time, a loss stroke motion takes place, whereby the parking brake does not work unless the moving distance exceeds the sum of the aforementioned distances H1 and H2. Since the loss stroke motion results in increasing the length of the conversion mechanism, a problem arises in that the large loss stroke movement causes the housing which accommodates the conversion mechanism and the equalizer, to be enlarged in dimension with an increase in the manufacturing cost for the electric parking brake device.